Словари

def get_coauthor_distance(name_dict, ref_name):
    """Возвращает список кортежей, описывающих расстояние между соавторами всех авторов в name_dict и автором ref_name.
 
    Аргументы:
    name_dict -- словарь, отображающий строку str в список str 
    ref_name -- автор ссылки как str
    """    
    # YOUR CODE HERE
    raise NotImplementedError()

sample_dict = {
    "author1" : [ "author2", "author3" ],
    "author2" : [ "author1", "author4" ],
    "author3" : [ "author1", "author4" ],
    "author4" : [ "author2", "author3" ]
}
get_coauthor_distance(sample_dict, "author3")
 
# result [('author3', 0), ('author1', 1), ('author4', 1), ('author2', 2)]
 
sample_dict2 = {
    "author1" : [ "author2", "author3" ],
    "author2" : [ "author1", "author4" ],
    "author3" : [ "author1", "author4" ],
    "author4" : [ "author2", "author3" ]
}
get_coauthor_distance(sample_dict2, "author0")
 
# result []
 
sample_dict3 = {
    "author1" : [ "author2", "author3" ],
    "author2" : [ "author1", "author4" ],
    "author3" : [ "author1" ],
    "author4" : [ "author2" ]
}
get_coauthor_distance(sample_dict3, "author3")
 
# result [('author3', 0), ('author1', 1), ('author2', 2), ('author4', 3)]

def get_coauthor_distance(name_dict, ref_name):
    if ref_name not in name_dict:
        return []
    result_tmp=coauthor_distance_help(name_dict, ref_name, level=0, result_tmp=[])
    result_tmp=sorted(result_tmp, key=lambda x: x[1]) 
    authors_known=set()
    result=[]
    for entry in result_tmp:
        author,score = entry
        if author not in authors_known:
            result.append(entry)
            authors_known.add(author)
        else:
            continue
    for author in name_dict:
        if author not in authors_known:
            result=[(author, -1)]+result
            
    return sorted(result, key = lambda x: (x[1], x[0]))
    
def coauthor_distance_help(name_dict, ref_name, level, result_tmp):
    if ref_name not in name_dict:
        return []
    for author, score in result_tmp:
        if author==ref_name: 
            if score<=level:
                return []      
    else:
        result=[(ref_name, level)]
        result_tmp+=[(ref_name, level)]
        #authors_known.add(ref_name)
        level+=1
        for author in name_dict[ref_name]:
            result+=coauthor_distance_help(name_dict, author, level=level, result_tmp=result_tmp)
    return result

def get_coauthor_distance(name_dict, ref_name):
    if ref_name not in name_dict:
        return []
    result_tmp=coauthor_distance_help(name_dict, ref_name, level=0, result_tmp=[])
    result_tmp=sorted(result_tmp, key=lambda x: x[1]) 
    authors_known=set()
    result=[]
    for entry in result_tmp:
        author,score = entry
        if author not in authors_known:
            result.append(entry)
            authors_known.add(author)
        else:
            continue
    for author in name_dict:
        if author not in authors_known:
            result=[(author, -1)]+result
            
    return sorted(result, key = lambda x: (x[1], x[0]))
    
def coauthor_distance_help(name_dict, ref_name, level, result_tmp):
    if ref_name not in name_dict:
        return []
    for author, score in result_tmp:
        if author==ref_name: 
            if score<=level:
                return []      
    else:
        result=[(ref_name, level)]
        result_tmp+=[(ref_name, level)]
        #authors_known.add(ref_name)
        level+=1
        for author in name_dict[ref_name]:
            result+=coauthor_distance_help(name_dict, author, level=level, result_tmp=result_tmp)
    return result